743 NOAA Technical Report NMFS SSRF- 743 .,>^^^'°'^o^^ Average Density Index for f ^ ^^ ^ \ Walleye Pollock, Theragra chalcogramma, in the c w O ^^.rEso^^^ Bering Sea Loh-Lee Low and Ikuo Ikeda November 1980 r Marine Biological Laboratory LIBRARY OCT 14 1992 Woods Hole, Mass. U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Marine Fisheries Service NOAA TECHNICAL REPORTS National Marine Fisheries Service, Special Scientific Report — Fisheries The major responsibilities of the National Marine Fisheries Service (NMFS) are to monitor and assess the abundance and geographic distribution of fisher>' resources, to understand and predict fluctuations in the quantity and distribution of these resources, and to establish levels for optimum use of the resources. NMFS is also charged with the development and implementation of policies for managing national fishing grounds, development and enforcement of domestic fisheries regulations, surveillance of foreign fishing off United States coastal waters, and the development and enforcement of international fishery agreements and policies. NMFS also assists the fishing industry through market- ing service and economic analysis programs, and mortgage insurance and vessel construction subsidies. It collects, analyzes, and publishes statistics on various phases of the industry. The Special Scientific Report — Fisheries series was established in 1949, The series carries reports on scientific investigations that document long-term continuing programs of NMFS, or intensive scientific reports on studies of restricted scope. The reports may deal with applied fishery problems. The series is also used as a medium for the publication of bibliographies of a specialized scientific nature. -NOAA Technical Reports NMFS SSRF are available free in limited numbers to governmental agencies, both Federal and State. They are also available in exchange for other scientific and technical publications in the marine sciences. Individual copies may be obtained (unless otherwise noted) from D822, User Services Branch, Environmental Science Information Center, NOAA, Rockville, MD 20852. Recent SSRF's are: 700. Expendable bathythermograph observations from the NMFS/ MARADShipof Opportunity Program for 1973. By Steven K. Cook. June 1976. iii -f 13 p., 10 figs. For sale by the Superintendent of Documents, US Government Printing Office, Washington, DC 20402; Stock No. 003- 01 7 -00382 -.5. 701. Seasonal abundance and distribution of zoopiankton, fish eggs, and fish larvae in the eastern Gulf of Mexico, 1972-74. By Edward D. Houde and Nicholas Chitty. August 1976, iii + 18 p., 14 figs., 5 tables. 702. Length composition of yellowfin, skipjack, and bigeye tunas caught in the eastern tropical Atlantic by American purse seiners. By Gary T. Sakagawa, Atilio L. Coan, and Eugene P. Holzapfel. August 1976, iv + 22 p., 7 figs., 7 tables, 15 app. tables. 703. Aquacultural economics ska. October 1976, 123 p. bibliography. By John Vondru- ments, U.S. Government Printing Office, Washington, DC 20402; Stock No. 003-020-00134-3. 712. Annual physical and chemical oceanographic cycles of Auke Bay, southeastern Alaska. By Herbert E. Bruce, Douglas R. McLain, and Bruce L. Wing. May 1977, iii + 11 p., 16 figs., 1 table. For sale by the Superintendent of Documents, U.S. Government Printing Office, Wash- ington, DC 20402; Stock No. 003-020-00134-3. 713. Current patterns and distribution of river waters in inner Bristol Bay, Alaska. By Richard R. Straty. June 1977, iii -I- 13 p., 16 figs., 1 table. 714. Wind stress and wind stress curl over the California Current. By Craig S. Nelson. August 1977, iii + 87 p., 18 figs., 1 table, 3 app. For sale by the Superintendent of Documents, U.S. Government Printing Of- fice, Washington, DC 20402; Stock No. 003-020-00139-4. 704. The macrofauna of the surf zone off Folly Beach, South Carolina. By William D. Anderson, Jr., James K. Dias, Robert K. Dias, David M. Cupka. and Norman A. Chamberlain. January 1977, iv -i- 23 p., 2 figs., 31 Ubles. 705. Migration and dispersion of tagged American lobsters, Homarus americanus, on the southern New England continental shelf. By Joseph R. Uzmann, Richard A. Cooper, and Kenneth J. Pecci. January 1977, v -I- 92 p., 45 figs., 2 tables, 29 app. tables. 706. Food of western North Atlantic tunas (Ttiunnus) and lancetfishes (Alepisaurus). By Frances D. Matthews, David M. Damkaer, Leslie W. Knapp, and Bruce B. Collette. January 1977, iii + 19 p., 4 figs.. 1 uble, 11 app. tables. 707. Monthly temperature and salinity measurements of continental shelf waters of the northwestern Gulf of Mexico, 1963-65. By Robert F. Temple. David L. Harrington, and John A. Martin. February 1977, iii + 26 p., 5 figs., 10 tables. 708. Catch and catch rates of fishes caught by anglers in the St. Andrew Bay system, Florida, and adjacent coastal waters, 1973. By Doyle F. Sutherland. March 1977, iii -I- 9 p., 2 figs., 9 tables. 709. Expendable bathythermograph observations from the NMFS/ MARAD Ship of Opportunity Program for 1974. By Steven K. Cook and Keith A. Hausknecht. April 1977. iv + 45 p., 10 figs., 9 tables, 35 app. figs. For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402; Stock No. 003 01 7 -00397 -3. 715. Bottom obstructions in the southwestern North Atlantic, Gulf of Mexico, and Caribbean Sea. By G. Michael Russell, Abraham J. Bar- rett, L. Steve Sarbeck, and John H. Wordlaw. September 1977, iii -f 21 p., 1 fig., 1 app. table. For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington. DC 20402; Stock No. 003- 020-00140-8. 716. Fishes and associated environmental data collected in New York Bight, June 1974-June 1975. By Stuart J. Wilk, Wallace W. Morse, Daniel E. Ralph, and Thomas R. Azarovitz. September 1977. iii + 53 p., 3 figs.. 3 tables. For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402; Stock No. 003-017- 0040-4. 717. Gulf of Maine-Georges Bank ichthyoplankton collected on ICNAF larval herring surveys September 1971-February 1975. By John B. Colton, Jr. and Ruth R. Byron. November 1977, iii + 35 p., 9 figs., 14 tables. 718. Surface currents as determined by drift card releases over the con- tinental shelf off central and southern California. By James L. Squire, Jr. December 1977, iii + 12 p., 2 figs. 719. Seasonal description of winds and surface and bottom salinities and temperatures in the northern Gulf of Mexico, October 1972 to Janu- ary 1976. By Perry A. Thompson. Jr. and Thomas D. Leming. Febru- ary 1978, iv + 44 p.. 43 figs., 2 tables. For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402; Stock No. 003-017-00414-7. 710. Midwater invertebrates from the southeastern Chukchi Sea; Species and abundance in catches incidental to midwater trawling survey of fishes, September-October 1970. By Bruce L. Wing and Nancy Barr, April 1977, iii + 43 p., 1 fig., 2 tables, 2 app tables. For sale by the Superintendent of Documents, U.S. Government Printing Office, Wash- ington, DC 20402; Stock No. 003-020-00130-1. 711. A list of the marine Rice. April 1977. iii + 15 p. mammals of the world. By Dale W. For sale by the Superintendent of Docu- 720. Sea surface temperature distributions obtained off San Diego. California, using an airborne infrared radiometer. By James L. Squire. Jr. March 1978. iii -^ 30 p.. 15 figs.. 1 table. For sale by the Superin- tendent of Documents. U.S. Government Printing Office. Washington, DC 20402; Stock No. 003-017-00415-5. 721. National Marine Fisheries Service survey of trace elements in the fishery resource. By R. A. Hall. E. G. Zook. and G. M. Mea- bum. March 1978. iii + 313 p., 5 tables, 3 app. figs., 1 app. table. ^''^r^^To^ NOAA Technical Report NMFS SSRF- 743 Average Density Index for Walleye Pollock, Theragra chalcogramma, in the Bering Sea Loh-Lee Low and Ikuo Ikeda November 1980 Marine Biological Laboratory ! LIBRARY f„ OCT 14 1992 Woods Hole, Mass. U.S. DEPARTMENT OF COMMERCE Philip M. Klutznlck, Secretary National Oceanic and Atmospheric Administration Richard A. Frank, Administrator National Marine Fisheries Service Terry L Leitzell. Assistant Administrator for Fisheries The National Marine Fisheries Service (NMFS) does not approve, rec- ommend or endorse any proprietary product or proprietary material mentioned in this publication. No reference shall be made to NMFS, or to this publication furnished by NMFS, in any advertising or sales pro- motion which would indicate or imply that NMFS approves, recommends or endorses any proprietary product or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or purchased because of this NMFS publication. CONTENTS Introduction 1 The walleye pollock fishery 1 Data base 2 Average density index 2 Topics of analysis 2 Examination for bias in the 1964-72 data base 3 Variability studies on pair trawl data 4 Comparison of ADIs from all-data versus pollock-majority-data 6 Index area-time cells 7 Trends in walleye pollock abundance 8 Summary 8 Acknowledgments 11 Literature cited 11 Figures 1. Mapof the Bering Sea showing statistical grids used in the Japanese ground fish data base 3 2. Four area-time cells used for calculating average density indices for walleye pollock in the eastern Bering Sea 7 3. Trends in catch per unit effort (CPUE) and average density index (ADI) for walleye pollock in the eastern Bering Sea, 1964-78 10 Tables 1. Annua! catch of walleye pollock, in thousand metric tons, in the eastern Bering Sea, 1964-78 2 2. Percentage of walleye pollock catches relative to total catches accounted for by major Japanese ves- sel-gear categories in the eastern Bering Sea, 1973-76 3 3. Statistics on variability studies on catch-effort data for pair trawlers in the 120-219 gross registered ton class in the Japanese surimi (a minced fish product) mothership fishery of the eastern Bering Sea, 1964-76 4 4. Statistics on variability studies on mean annual catch per unit effort (CPUE) of walleye pollock by pair trawlers of the 120-219 gross registered ton class in the Japanese surimi (a minced fish product) mothership fishery in the eastern Bering Sea, 1964-76 6 5. Average density indices, in metric tons per hour trawled, for all-data versus walleye pollock- major- ity-data by vessel-gear categories in the eastern Bering Sea, 1973-76 6 6. Number of major statistical block months in which average density indices computed from all-data versus walleye pollock-majority-data in the eastern Bering Sea were the same, differed by 0.1, or dif- fered by more than 0.1 metric tons per hour trawled 6 7. Comparison of average density indices, in metric tons per hour trawled, for walleye pwllock in the eastern Bering Sea by area-time cells (see Figure 2 and text) and vessel-gear categories, 1973-76 .... 9 8. Annual average density indices (ADIs; in metric tons per hour trawled) and relative ADIs (as percent- age of 1976 ADI) for walleye pollock in the eastern Bering Sea by area-time cells (see Figure 2 and text) and vessel-gear categories, 1973-76 10 9. Overall average density indices (ADIs; as percent of 1976 metric tons per hour trawled) for walleye pollock in the eastern Bering Sea computed from ADIs in area-time cells which were weighted by catches, 1973-76 10 111 Average Density Index for Walleye Pollock, Theragra chalcogramma, in the Bering Sea LOH-LEE LOW' and IKUO IKEDA' ABSTRACT The data base and an average density index (ADD procedure for assessing walleye pollock. Theragra chalcogramma. abundance in the eastern Bering Sea were evaluated. The data base con- sisted of daily catch-effort records of individual fishing vessels in the Japanese groundfish fishery from 1%4 to 1976. Variances about the annual mean catch, effort, and catch per unit effort (CPUE) data were low. Coefficient of variation of annual CPUE data was in the \-2% range for the data base after 1%9 but higher in earlier years when the number of fishing records was lower. An ADI procedure is de- scribed which takes into consideration different types of vessels used in the fishery, species mix in the catch, distribution uf pulhuk. and fishing pattern of the fieel. Data from five vessel class-gear types that fished mainly for pollock were selected to compute ADIs in four area-time cells. An overall ADI within these cells was determined, summarizing the results by vessel class-gear types and area-time cells. From l%4 to the early IHTDs, overall ADI and CPUE trends increased as a result of increased pol- lock abundance and fishing power of vessels. For 2-.'J years during the early 1970s, abundances of pol- lock were at peak levels. Beginning in 1972, abundance declined but stabilized during 1975-78 at an intermediate level when 1.1 million metric tons of walleye pollock were harvested annually. INTRODUCTION Catch-eflort data from commercial fisheries can be very useful for monitoring abundance of fish stocks. The concept for its use is simple: if conditions of fishing and vulnerability of the stock to fishing remain fairly con- stant, the amount of catch for a standard unit of fishing effort, catch per unit effort (CPUE), should reflect abun- dance of the stock under exploitation (FAO f976). However, conditions of the fishery and dynamics of the stock (and therefore its vulnerability to fishing) fre- quently change, complicating the use of CPUE. These chan'ges and the quality of data are variables that may invalidate the use ot CPUE for measuring stock abun- dance. It is, therefore, of great importance to collect and analyze catch-effort data carefully so that these and other factors do not bias indices of abundance. In the eastern Bering Sea, catch-effort data from the Japanese trawl fishery have been the most consistent and important source of information for assessing walleye pollock, Theragra chalcogramma, abundance. Since 1964, these data have been collected in a detailed and systematic manner. From this data base, CPUE computations to assess abundance of the pollock resource have been made over several years and results reported in documents submitted to the International North Pacific Fisheries Commission (INPFC). At the 1974 annual meeting of the INPFC, Japanese scientists presented an extension of the CPUE index used by U.S. scientists as a measure of pollock abun- dance termed an average density index (ADI). This ADI procedure involved some selection of pair trawl catch- effort data from the data base for its computations. Because the Japanese trawl fishery used various vessel- gear combinations and took a variety of species, there was some difficulty in data selection for deriving un- biased measures of pollock abundance. In addition, there was a need to evaluate whether the fundamental data is representative of all data collected since not all daily catch-effort records were incorporated into the data base used to derive ADI values. To resolve these questions, the Committee on Biology and Research of INPFC es- tablished a working group to evaluate the data and the ADI procedure for assessing pollock abundance. This paper reports on results of the working group's study on the bias and variability of catch-effort data and the stan- dardization of ADIs as a measure of pollock abundance. THE WALLEYE.POLLOCK FISHERY Walleye pollock is of the family Gadidae and is dis- tributed throughout the North Pacific. Its life span is about 15 yr, but 2-6 yr olds are the major ages exploited by the fishery. This age range corresponds to fish weigh- ing 91 g (24 cm fork length) and 817 g (49 cm fork length). Pollock is by far the most abundant demersal fish in the eastern Bering Sea (Pereyra et al. 1976)^ and has been 'Northwest and Alaska Fisheries Center, National Marine Fisheries Service. NOAA. 2725 Montlake Boulevard East, Seattle, WA 98112. "Far Seas Fisheries Flesearch Laboratory, Fisheries Agency of .Japan, 1(100 Orido, Shimizu 424, Japan. 'Pereyra, W. T., J. E. Reeves, and R. G. Bakkala. 1976. Demersal fish and shellfish resources of the eastern Bering Sea in the baseline year 1975. Processed Rep., 619 p. Northwest and Alaska Fish. Cent., Natl. Mar. Fish. Serv., NOAA. 2725 Montlake Boulevard E., Seattle, WA 98112. the major target species of foreign trawl fisheries there. It supports the largest single species fishery in the North Pacific. The modem history of groundfish exploitation in the Bering Sea began in 1954, but the fishery for pollock did not begin in earnest until the early 1960s. At that time yellowfin sole, Limanda aspera, declined substantially in abundance (Forrester et al. 1978) and in 1964 mechanized techniques for processing pollock into suri- mi (a minced fish product) were successfully imple- mented on Japanese motherships and large factory stern trawlers (Bakkala et al. In press). As a result pollock catches increased more than tenfold between 1964 and 1972 (from 175,000 t to nearly 1.9 million t. Table 1). Catches declined steadily thereafter to <1 million t in 1977-78 due to declining stock abundance and fishery re- strictions on the catch. This trend in stock abundance was generally monitored by CPUE data from the fish- ery, but the ADI procedure appeared to be a good measure of abundance as well. They both depended on data compiled from the Japanese trawl fisheries in the Bering Sea. Table 1. — Annual catch of walleye pollock, in thousand metric tons, in the eastern Bering Sea, 1964-78. Republic Year' Japan USSR' of Korea Taiwan Total 1964 175 _ 0 0 175 1965 231 — 0 0 231 1966 262 — 0 0 262 1967 550 — 0 0 560 1968 701 — 1 0 702 1969 830 27 5 0 862 1 971) 1,231 20 5 0 1,256 1971 1.514 220 10 0 1,744 1972 1,651 214 9 0 1,874 1973 1,476 280 3 0 1,759 1974 1,253 310 26 0 1,589 197.5 1.137 217 3 0 1,357 1976 913 179 85 0 1,177 1977 869 63 45 1 978 1978 821 93 62 3 979 Data fnr 1964-76 were reported by respective nations to the U.S. Na- tional Marine Fisheries Service. Data for 1977-78 were estimated by the U.S. National Marine Fisheries Service. "Union oi" Soviet Socialist Republics. DATABASE ADI = (KA X On/iZA Major nations participating in the pollock fishery are Japan, Union of Soviet Socialist Republics, Republic of Korea, and Taiwan (Table 1). Japan has accounted for more than 85"^ c of walleye pollock catches (Forrester et al. 1978) and since 1964 has collected more detailed and complete catch-effort records on her fisheries than any other nation. It is this data base of catch-effort records where we place great reliance for monitoring stock abun- dance. The fundamental data collected were daily catch- effort statistics by species or groups, within statistical blocks (1° longitude by '2° latitude, Fig. 1), and by in- dividual fishing vessels and gear type. Vessels were further classified according to 10 tonnage classes from 1 to 4,500 gross registered tons (GRT). Major gear types were pair trawls, Danish seines, side trawls, longlines, gill nets, and stem trawls. For 1964-72, many daily catch-effort records for in- dividual vessels were not incorporated by the Fisheries Agency of Japan into the data file for economic reasons. Rather, every third record of such records was selected for key-punching. These subsampled records were then extrapolated to represent the total fishery. Since 1973 all catch-effort records have been included in the data base. The total data base is maintained by the Fisheries Agency of Japan. Monthly summaries of the catch-effort information by statistical blocks by fishing gear type and vessel size class were subsequently made available to the United States and Canada as member nations in INPFC. AVERAGE DENSITY INDEX The ADI equation presented at the 1974 INPFC meeting by Japanese scientists^ was as follows: where i = a statistical block number, A = area (km-) of each statistical block , 0 = catch per unit effort in metric tons per hour trawled within each statistical block. The application of this procedure for walleye pollock involved some selection of catch-effort data from pair trawlers which they determined to be the most consistent gear type directed to pollock fishing activities in each statistical block. Statistical blocks used in the calcula- tions were those where the daily pollock catch was greater than that of any other species. From these selected "pollock-majority" catch-effort data an ADI was computed for an area made up of several statistical blocks. TOPICS OF ANALYSIS Objectives of our study were to evaluate the data base and procedures used for calculating ADIs for pollock. Specifically, we chose four topics to: 1) determine if bias towards high or low catches was introduced in the data base by subsampling of daily data records during 1964-72; 2) conduct variability studies in pair trawl data used for ADI and CPUE computations; 3) compare pollock ADIs calculated from all-data and pollock-majority-data; and 4) identify area-time cells for more accurate assess- ment of pollock abundance. 'Fishery Agency of Japan. 1974. Pollock stocks in the eastern Bering Sea. Unpubl. manuscr.. 38 p. Far Seas Fish. Res. Lab., 1000 Orido, Shimizu 424, Japan. JAPANESE BERING SEA GROUNDFISH Vi X 1 degree statistical blocks ^ ■S Vi , \ ■V.V1 r ^ n MBL = major statistical block S; - 1 1 V-/ ■J 1 1 1 ~ "^"TT^ 1 1 1 : tC V ' 0^ 1 j ^J j) MBL 45 MBL 35 PMBL2E /"^ ) 1 1 1 1 ^ 1 . 100 meters _ ^ ^ ■^, ^ ;~ ■ 1 1 1 i P i \ ~ -■ \ J •■ / 1 2UU meters 2000 meters f >P- /"^ .^ / 1 / MBL 34 MBL 24 \ ^ -O^ / t'f MBL 54 h, MBL44 i — — — < ii // Ft V 1^ MBL64 ^. 't-.,. L-J i ^ f ^J ; 1 i 1 '■\...-, ; V- j~ t/^ ~^ ^ '^\ ^' l_ 1 i • MBL43 MBL 33 MBL 23 MBL 13 ^ . MBL 73 MBL 63 [MBL 53 "" "" — ' \: :, i U'\ n .L 1 ' 1 V i- -\ ^j < fl ) / f ' \ i 1 1 1 1 MBL 52 MBL 42 'v MBL 32 ^ MBL 22. MBL, 12 1 I. MBL 72 MBL 62 "iV ! o ; ^ A A ) ' ' I.- •»'" /j' / 1 f ' — 1 i r^ / 7 y1 ""a s 0 V v<. fi ■v /-. U r ^1 ' '" ^ i 1 f^^ ' "1 MBL 61 MBL 51 MBL 41 j 1 MBL 31 1 V1BL21^ "> tf 'z M SL 71 ' 1 .:M- " 1 f [i >• _, '' ^ -- • '' ^" o"- 1 r »o 1 _. V J^V ^_i- 'n, ^ 7i,,--;^r^ ^'j :>- - ' N f^^ s^ fo' 1 M --r 1 — _^ _ _ L- _ ■ 1 1 ! J 60° N 55° N 165° E 170° E 175° E 180° 175° W 170° W 165° W 160° W Figure 1.— Map of the Bering Sea showing statistical grids used in the Japanese groundflth data base. EXAMINATION FOR BIAS IN THE 1964-72 DATA BASE Since the data base for 1964-72 included only a third of the daily catch-effort records, we wanted to determine whether the partial data base is biased towards high or low catch levels by the subsampling procedures used. It was necessary to examine this question indirectly by us- ing the complete 1973-76 data base because the missing records in the earlier 1964-72 data could not be easily restored. First we subsampled the 1973-76 data on pair trawlers in the same manner in which the 1964-72 data was created so as to create an equivalent file of one-third the daily fishing records. Pair trawl data were used because we determined that the vessels consistently ac- counted for the largest proportion (38'r) of the walleye pollock caught, and should be most representative of pol- lock fishing activities (Table 2). As a result of this sub- sampling, two data files were created: a one-third pair trawl file and an all pair trawl file. We compared these two files by testing if their monthly mean catch and effort data were statistically the same. This was achieved by (-tests of two means when their variances were unknown (Snedecor and Cochran 1967). The tests showed that the null hypothesis (that mean catch and effort of both data files were the same) was not rejected at the 5' r level in all cases. Based on these tests, we concluded that subsampling of the 1964-72 data base probably resulted in a random sample of the population and was not biased towards high nor low catches. Table 2.— Percentage of walleye pollock catches relative to total catches accounted for by major Japanese vessel-gear categories in the eastern Bering Sea, 1973-76. 1973 1974 1975 1976 Type 1— Pair trawlers, 120-219 CRT 35 37 35 36 Type 2 — All pair trawlers 39 37 38 37 Type 3— Stem trawlers. <300 CRT 4 5 7 6 Type 4— Factory trawlers. 1.500-3.500 CRT 9 10 10 9 Type 5— Factory trawlers. >3.500 GRT 28 26 27 28 GRT = gross registered tons. Source: Fisher>' Agency of Japan. VARIABILITY STUDIES ON PAIR TRAWL DATA Because the data records of Japanese groundfish catch-effort statistics that were available through INPFC were summaries of many daily trawls, variances about these statistics cannot be estimated. Therefore, we estimated variances of the fundamental daily catch, effort, and CPUE data for statistical interpretation of CPUE values. We selected the 120-219 GRT class of pair trawlers attached to the Japanese surimi mother- ship fishery for the analysis because these trawlers were probably the most representative vessels used in the fishery for monitoring pollock CPUE trends (Table 2). The analysis by monthly and annual periods shows that standard deviations of mean catch, effort, and CPUE values decreased substantially after 1973 when the number of daily catch-effort records (sample size) were increased from earlier years (Table 3). Variances about the monthly and annual CPUE values calculated from daily catch-effort records were small after 1965. Co- efficient of variation (CV) for the 1964 and 1965 data was 19''c and d'^'c. when the sample sizes were small (Table 4). When the sample size approached 300 (1966-69), CV generally was below 4'^i. As the sample size increased and approached 5,000 (1970-76) the CV decreased to the 1-2% range. A comparison of annual mean CPUEs at the 95% con- tidence level shows that pollock CPUE increased signifi- cantly each year from 1963 to 1969, followed by a sig- nificant decrease from 1969 to 1971 (Table 4). Another Table 3.— Statistics on variability studies on catch-effort data for pair trawlers of the 120-219 gross registered ton class in the Japanese surimi (a minced fish product) mothership fishery in the eastern Bering Sea, 1964-76. Mean Sample Mean Standard Mean Standard catch per Standard Year Month size' catch' deviation effort' deviation effort* deviation 1964 5 7 240 51 38.7 2.0 6.32 1.41 6 6 195 31 45.8 6.4 4.20 .45 7 6 475 118 33.3 2.0 13.79 2.67 8 4 82 64 35.5 9.0 4.13 3.20 9 7 0 0 29.1 2.5 .00 .00 Annual 30 201 40 36.4 2.0 5.62 1.11 1965 5 14 195 24 14.9 1.8 14.05 1.90 6 6 156 32 16.7 1.1 9.76 2.19 7 6 265 19 20.0 1.3 13.47 1.20 8 10 284 15 20.2 .6 14.22 .88 9 12 40 6 14.4 .8 2.78 .32 Annual 48 178 16 16.7 .7 10.66 .94 1966 5 20 198 11 23.4 .4 8.59 .57 6 16 183 17 23.6 .4 7.86 .83 7 20 168 13 24.0 .0 7.02 .54 8 20 153 17 23.1 .6 7.04 .96 9 16 84 12 22.9 1.8 3.74 .50 Annual 92 159 7 23.4 .4 6.94 .35 1967 3 30 319 30 41.8 1.6 7.77 .70 4 30 540 42 24.9 1.6 23.66 2.22 5 46 340 30 43.9 2.4 7.87 .49 6 50 347 32 43.9 2.6 7.66 .57 7 55 583 47 48.3 3.0 11.96 .50 8 50 674 57 44.1 2.9 14.35 .49 9 44 475 52 37.1 2.9 12.76 .92 Annual 305 477 18 41.7 1.1 11.88 .41 1968 3 36 831 56 30.5 1.7 30.90 2.83 4 50 644 41 34.5 1.3 20.47 1.75 5 78 692 36 35.9 1.6 20.08 .94 6 80 743 48 40.0 1.8 19.74 1.29 7 82 705 38 28.2 1.3 26.90 1.49 8 83 798 47 34.8 1.7 23.71 1.14 9 74 683 40 32.7 1.6 21.82 1.14 10 15 649 103 35.7 4.0 18.91 2.22 Annual 498 723 17 34.1 .6 22.80 .53 1969 3 39 947 67 13.8 .9 80.89 7.55 4 55 807 57 26.7 1.7 37.74 3.37 5 75 594 41 38.2 2.1 18.85 1.65 6 79 565 53 47.2 1.7 11.41 .91 7 88 848 50 45.3 1.9 18.64 .86 8 78 976 60 26.0 1.6 41.33 2.25 9 61 980 67 31.7 2.1 33.45 1.66 Annual 475 802 22 34.8 .8 30.42 1.24 Table 3.— Continued. Mean Sample Mean Standard Mean Standard catch per Standard Year Month size' catch" deviation effort' deviation effort' deviation 1970 3 68 1,335 79 25.7 1.4 64.23 5.36 4 110 841 51 37.8 1.9 24.73 1.40 5 160 537 34 42.2 1.5 13.74 .83 6 202 851 35 44.3 1.5 20.26 .63 7 205 1,070 41 37.2 1.5 32.52 .97 8 199 909 41 42.3 1.4 22.74 .77 9 181 898 41 38.0 1.3 23.99 .71 10 24 257 32 23.6 .8 10.89 1.26 Annual 1,149 879 17 39.3 .6 25.39 .56 1971 3 113 1,121 56 29.1 1.3 43.46 2.43 4 157 1,375 53 38.0 1.3 45.20 2.84 5 249 782 29 46.5 1.2 21.07 1.21 6 252 763 24 55.5 1.1 14.39 .52 7 271 1,005 33 54.7 1.1 19.54 .73 8 263 1,260 30 54.2 1.2 24.59 .60 9 219 1,104 32 49.6 1.3 23.30 .57 10 18 531 60 23.3 1.8 23.63 2.41 Annual 1,542 1,028 14 48.8 .5 24.75 .50 1972 3 125 1,442 68 25.5 1.0 61.13 2.87 4 169 1,480 56 26.9 1.0 67.20 3.14 5 329 713 25 46.3 1.0 16.29 .56 6 329 725 27 45.8 1.1 16.87 .64 7 342 1,241 33 45.2 1.1 30.26 .95 8 321 1,331 42 43.0 1.1 34.26 1.06 9 262 1,020 37 39.6 1.2 26.75 .64 Annual 1,877 1,078 16 41.4 .5 31.04 .59 1973 3 417 973 26 39.3 .5 26.13 .74 4 555 985 20 51.9 .4 19.51 .42 5 712 617 15 55.4 .7 11.60 .36 6 920 729 20 51.7 .7 14.00 .34 7 981 1,259 20 47.6 .6 28.35 .38 8 964 1,088 16 44.7 .6 27.65 .44 9 804 1,036 18 43.2 .8 28.00 .49 Annual 5,353 968 8 48.0 .3 22.39 .19 1974 4 590 1,013 19 38.6 .5 27.89 .60 5 772 608 10 48.5 .5 12.99 .20 6 1,046 727 10 45.8 .5 17.28 .31 7 1,083 840 12 48.9 .6 18.85 .27 8 1,068 853 12 50.7 .7 18.32 .22 9 981 983 16 44.8 .7 24.55 .38 10 20 655 36 43.4 1.7 15.76 1.27 Annual 5,560 832 6 46.8 .3 19.59 .14 1975 3 3 763 281 29.7 2.9 26.30 9.14 4 391 634 15 43.8 .6 14.86 .34 5 790 525 9 45.0 .5 11.78 .18 6 1,019 614 8 45.9 .5 14.02 .17 7 1,048 772 10 50.7 .6 16.88 .26 8 1,034 798 9 45.1 .6 20.64 .41 9 875 767 15 41.7 .5 18.24 .30 10 150 615 17 43.5 .9 14.83 .48 Annual 5,310 695 4 45.6 .2 16.33 .12 1976 4 267 486 14 47.7 .5 10.74 .36 5 737 446 8 54.7 .4 8.37 .16 6 840 678 7 53.3 .5 13.94 .22 7 867 864 8 49.0 .5 19.14 .26 8 824 947 10 43.8 .5 24.54 .46 9 743 756 9 37.5 .5 22.38 .36 10 545 772 11 42.6 .5 19.10 .32 Annual 4,823 734 4 47.2 .2 17.54 .15 Sample size is number of daily catch-effort records. "Catch in 0.1 metric tons. Effort in 10-min trawling. Catch per unit effort in metric tons per 100-min trawling. Table 4. — Statistics on variability studies on mean annua) catch per unit effort 3.500 GRT. Table 6.— Number of major statistical block months in which average density indices computed from all-data ver- sus walleye pollock-majority data in the eastern Bering Sea were the same, differed by 0.1, or differed by more than 0.1 metric ton per hour trawled. Vessel class-gear 1973 differences 1974 differenci es 1975 differences 19- "6 differences type ' Total None 0.1 >0.1 Total None 0.1 >0.1 Total None 0.1 >0.1 Total None 0.1 >0.1 1 29 21 3 5 30 24 4 2 31 31 0 0 31 28 0 3 2 29 22 2 5 30 23 5 2 31 30 1 0 31 28 0 3 3 25 24 1 0 33 21 5 7 37 34 1 2 41 40 1 0 4 57 49 3 5 52 48 0 4 47 46 0 1 52 50 1 1 5 65 56 5 4 64 51 4 9 59 52 4 3 60 56 1 3 'Type 1 — Surimi la minced fish product) mothership, pair trawlers, 120-219 gross registered tons (GRT). T>"pe 2 — Surimi mothership, all pair trawlers. Type 3 — Surimi mothership. stern trawlers, <300 GRT. Type 4 — Surimi factory stern trawlers. 1.500-3,500 GRT. Type 5 — Surimi factory stern trawlers, >3,500 GRT. MBL-months, the two sets of ADIs were similar and 2) the frequency and magnitute of observed differences were fewer and lower in the most recent years. We found that differences occurred most frequently in the south- eastern Bering Sea (MBLs 21 and 22) during March- June for pair trawlers and in the central and northern Bering Sea (MBLs 32, 33, 43, and 44) during December- March for factory trawlers. These differences occurred in times and areas where species other than pollock were caught in large quan- tities. As the proportion of species other than pollock in- creased in the catch, differences became greater. The differences, however, were not significant although ex- clusion of data from poor pollock catches by one criterion resulted in ADIs that were on the high side and inclusion of all data by the other resulted in lower ADIs. Since we cannot distinguish which ADI was truly indicative of pollock abundance and not biased by changed in species composition, it was necessary to define index area-time cells which more accurately reflect trends in abundance. INDEX AREA-TIME CELLS Based on distributional pattern of pollock and its life history features (Pereyra et al. 1976 see footnote 3) we identified four area-time cells (Fig. 2) which consistently accounted for high proportions (75% or more) of pollock in the catch for ADI computations. Area-time cell I — MBLs 21 and 22, March-May, which represents the main spawning area during the spawn- ing period. Area-time cell II — MBLs 21 and 22, July-Septem- ber, which represents the main spawning area during a feeding period. AREA-TIME CELLS BL 21 and 22, March-May MBL 21 and 22, July-September BL 32 and 33, April-July MBL 43 and 44, June— September major statistical block) 60° N 55° N 180° ' 175° W 170° W 165° W 160° W Figure 2.— Four area-time cells used for calculating average density indices for walleye pollock in the eastern Bering Sea. Area-time cell III Area-time cell IV MBLs 32 and 33, April-July, which represent the transitional area (between spawning and feeding grounds) during a transi- tional period (between spawning and feeding periods). MBLs 43 and 44, June-Septem- ber, which represents the north- em feeding area during a feeding period. Each area-time cell was selected to delineate a unique phase of the distribution of the pollock population during the year. From catch distribution patterns, we also deter- mined that these phases of distribution were usually repeated during the same area-time cell each year, there- by providing comparability of ADIs from year to year. After the selection of these four area-time cells, ADIs were computed for all vessel-gear categories except Type 2, which was already considered in Type 1. The computa- tions were made using all-data as opposed to pollock- majority-data within each cell because their results were not expected to be significantly different. The equation used to determine these ADIs was: ADI^ = (""2 (A,^ X 0^))/(""2A^) where a = 1,2,3,4 index area-time cells g = 1,2,3,4 vessel-gear types i = 1,2, . . . n statistical block number riu = number of statistical blocks selected for computation in index area-time cell a O^g = catch per unit effort (metric tons per hour trawled) by gear-vessel type g in statistical block i within index area-time cell a A„j = area (km-) covered by vessel-gear type g which is made up of statistical blocks i within area-time cell a. (Table 9). Most of the decline occurred between 1973 and 1974, and from 1974 to 1976 relative abundance remained fairly stable. TRENDS IN WALLEYE POLLOCK ABUNDANCE Since we analyzed the 1964-76 data base at the working group meeting in 1977, we have updated the analyses on annual CPUE and ADI trends through 1978 as shown in Figure 3. They are trends of pair trawl data from the surimi mothership fishery. From 1964 to the early 1970s, there was a general increase in the CPUE and ADI trends which resulted from increased pollock abundance and fishing power of vessels. Catch composi- tion and trends (Forrester et al. 1978) showed that pol- lock became increasingly abundant as the fishery pro- gressed in the 1960s. At the same time, there must have been considerable learning experiences by fishermen which contributed to higher CPUEs as noted by Lx)w (1974). Technological changes in the fishing fleet also took place, which no doubt increased the size and overall efficiency of fishing vessels. Effects of these physical changes on CPUE and ADI trends were probably held rather constant by selecting data from our five standard vessel class categories for computations. However, we cannot separate the effect of increased fishing pow- er of vessels from the effect of increased pollock abun- dance in CPUE and ADI trends from 1964 to the early 1970s. For 2-3 yr during the early 1970s, abundance of pollock appeared to be at peak levels. By this time most of the technological changes and human learning factors that contributed to increased fishing power have probably stablized. Beginning in 1972, both CPUE and ADI trends decreased but stabilized during 1975-78 at an intermedi- ate level when 1.1 million t of pollock were harvested an- nually. The results shown in Table 7 are ADIs calculated by the above equation from monthly data by vessel-gear type within each cell. A summarization of these monthly ADIs by cell and gear type is presented in Table 8. In this table, ADIs were weighted by the magnitude of catches and then expressed in percentages relative to 1976 pair trawl ADIs. In the interpretation of ADI trends within area-time cells we also considered changes to the accustomed fish- ing pattern due to factors such as fishing regulations. Area-time cell I probably would not provide a good in- dicator of pollock abundance for 1973-76 because that cell was partially closed to trawling during some years (INPFC 1979). Time-area closures have not been a factor in the other three cells (U-IV) and fishing patterns did not change significantly during 1973-76. Thus, ADIs were better indicators of stock abundance in these latter three cells than in cell I. The trend in ADIs shows that relative pollock abun- dance declined from 1973 or 1974 to 1976 in all cells SUMMARY The data base and an average density index (ADI) procedure for assessing abundance of walleye pollock in the eastern Bering Sea were evaluated. This data base was made up of daily catch-effort records of individual fishing vessels in the Japanese groundfish fishery. For the period 1964 through October 1972, the data base consisted of a third of the total daily catch-effort rec- ords. Thereafter, all daily records were included. Based on pair trawl data from the 120-219 gross registered ton class of vessels in the surimi mothership fishery, it was determined that one-third of the records provided a statistically representative sample of the entire data base. It was further determined that monthly sum- maries of daily catch-effort records that have been sub- mitted by Japan to INPFC and used by U.S. scientists for assessing abundance of walleye pollock were not sig- nificantly different from daily records used by the Fish- eries Agency of Japan in their assessments. be >> u — tc .9 H S'S a 01 B S E S f 2 c H (M q: en c >* o o O in CO A 's 'C 3 tn a> S CO E- -M o o £" »o o u to to 3 iC t~- CM CM § ■-* t-^ CD 00 3 r- rj- ^ o i 00 t~- 00 ^2 _>j ootoiqo *;cM.-icooj 3aioodt^ S'cocoirioo >) c^ t~- to Ol CD 00 00 aJ CM 00 00 Oi t^ g CD tq CO »r; n t-- iri "^ c-^ ei 00 CD CO 3 co' . CO— "COC^ >. ^int^QO 00 to CD >C O CD — ' UO ^ t> oi CO >. 1— ' lO O I 3 CO t-H C?> I 1-3 -^ •-< ■^ 00 05 CO -i- CO r- "tj- lO -^ CO CM E-~ O • O E-~ CD ifi CS CD CO 00 CJS CD iC -^ 3 CD * t-^ p t-^ CO 3 00 lO Tj- r-^ CM p 00 p txj ■^ -^ C3 - S. 3 _( Tf 00 CD CO CD »rj iri ■ t~- — . [- CO uri CD cm' c^ —' a,^. ^^. ^. '^. r-^ CD "^ CO 05 iC CO CO -^' t-^ i/i CD UO ,^ I 1 COC^CMiC tiLoOCDOO 00 00 "^ »C CO CM in CD CD 3 t- »C "* CO O iC CM to ' CO m CM CO CO CD -^ CO r^ t- m t^ O 00 CD Q-O cd ^ 3 oi co> CD lO CO iq iri CO ^ t-^ I ^ 3 (X> C- CM -^ '" CO oi -^ CO CM OS CM 00 00 CD rf in ^ 0> CO tT -rp -2 CM t-^ CO CO CD O C^ lO t>^ CD "d- "* CD p Ol CD r- t~ ic CO CM O) COOOCD 3cMCDCMI^ 0) CD be 00 I I CO O CO no • r-^ o "^ -^ cooqr- flBt~;"*icp j:^cMCM--;.-H couocM ^oiiccMco .^ocduo-^ CO --; CD CD oi r- CM CO CM CO 00 CO Ol ^ 't^oio <;aoi>r-Tr C CO 00 p "-; 3 t~^ lO ifj lO -I 5 ; 00 p iC UO i 05 O) t~ '^ 00 Oi Ol aoqoqpp ^.-Hpcqp i,^^_ji,'j CooOOOOO CicoOiO 3 O — ' CO ic c ^ o oi crj >i r~ Oi o r- 3 CD O oi CJ ■-1 OS OO CO • ic -^ oi --* H cr: >. in 1" CM 00 CO D. ■^ OO Ol 3 O •-3 "^ c- CD CO CO CM CO t: °° Ol m ■<* 00 CD 00 1^ ^S CM 00 CD 3 < --. Oi t- l5 1 1 1 >. 1 CO oi p d 15 tji CM CM 00 CO 3 liO oi i-i CO ■< ^ ,— I -H >i Ol CD CO r- 3 -^ CO CO 00 COCDt~- c'^*'?^^ t-^inic a^oiodcd co-t-ocD _cO"*iCCO KcO"finco >'CO-rif; ^— OlOlOlOl — OIOIOIOI . — .OlOlOiOi —^^GiSi CO -^ iC CD i> i> r~ r- Ol Ol Oi Ol u Table 8. — Annual average density indices (ADIs; in metric tons per hour trawled) and relative ADIs (as percentage of I97S ADD for walleye pollock in the eastern Bering Sea by area-time cells (see Figure 2 and text) and vessel-gear categories, 1973-76. Mothership pair Mothership stem Factorv stern trawlers Factory stern trawlers trawlers (120-219 GRT)' Catch Relative trawlers (<300 GRT) Catch Relative (1,500-3,500 GRT) Catch Relative 03,500 GRT) Gear Relative summary time Catch Relative Standard cell (l.OOOt) ADl ADl (l.OOOt) ADl ADl (l,000t) ADl ADl (l.OOOt) ADl ADl ADl ADl' Cell I 1973 124 9.8 218 19 6.6 194 17 7.0 179 41 9.7 107 204 9.2 1974 88 9.9 220 5 9.7 285 4 6.4 164 21 6.2 119 202 9.1 1975 19 7.5 167 7 4.2 124 4 4.8 123 16 5.9 113 147 4.4 1976 23 4.5 100 6 3.4 100 6 3.9 100 27 5.2 100 100 4.5 Cell II 1974 31 12.8 92 27 6.6 67 39 7.5 127 87 10.5 131 114 15.8 1975 78 10.9 78 39 7.8 80 33 7.6 129 73 10.1 126 102 14.2 1976 98 13.9 100 38 9.8 100 26 5.9 100 70 8.0 100 100 13.9 Cell III 1973 112 10.8 124 14 8.2 141 0 9.0 180 36 10.7 173 140 12.0 1974 126 8.8 107 17 6.9 119 12 6.6 138 28 7.3 118 108 9.3 1975 152 8.0 93 9 4.2 72 14 5.3 110 38 6.3 102 95 8.2 1976 105 8.6 100 18 5.8 100 U 4.8 100 30 6.2 100 100 8.6 Cell IV 1973 258 15.1 1.39 61 7.6 169 41 8.2 82 170 11.5 140 140 15.3 1974 181 10.0 92 10 6.0 133 8 4.0 40 36 7.7 94 92 10.0 1975 56 9.6 88 10 4.7 104 3 4.8 48 8 6.2 76 87 9.5 1976 69 10.9 100 4 4.5 100 1 10.0 100 8 8.2 100 100 10.9 Cell summary 1973 517 11,0 105 120 7.6 115 122 8.1 145 420 10.7 134 121 12.7 1974 462 10.1 96 104 7.0 106 122 6.4 114 335 8.4 105 102 10.7 1975 369 9.3 89 105 5.9 89 112 5.8 104 277 7.1 89 91 9.6 1976 354 10.5 100 99 6.6 100 89 5.6 100 263 8.0 100 100 10.5 'GRT is gross registered tons. 'Standardized to mothership pair trawler ADl units. Tables— Overall average density indices (ADIs; as percent of 1976 metric tons per hour trawled) for walleye pollock in the eastern Bering Sea computed from ADIs in area-time cells which were weighted by catches, 1973-76. Feeding season, Transitional season. Feeding season. southern area transitional area northern area (Area-time cell II) Catch Relative (Area-time cell III) Catch Relative (Area-time cell IV) Catch Relative Summary Catch Relative Year (l,000t) ADl (l,000t) ADl (l.OOOt) ADl (l.OOOt) ADl 1973 0 — 170 140 530 140 700 140 1974 184 114 183 108 235 92 602 104 1975 223 102 213 95 77 87 513 97 1976 232 100 164 100 82 100 478 100 ^jiT^t-srs- ,00 Q Variances about the monthly and annual means of catch, effort, and catch per unit effort (CPUE) calcu- lated from the daily records were small for most years. In 1964 and 1965 when the number of daily records was small, the coefficients of variation were 19% and 9%. As the annual sample size of daily records approached 300, coefficients of variation for CPUE generally declined to below 4'^c, which was about the level for the data from 1966 to 1969. As the fishery expanded after 1969 and the number of daily fishing records approached 5,000; coef- ficients of variation were reduced to between 1% and 2%. Figure 3.— Trends in catch per unit effort (CPUE) and average den- sity index (ADl) for walleye pollock in the eastern Bering Sea, 1964- 78. 10 Catch-effort records of two types have been used for calculating ADIs: 1) records where walleye pollock were the most abundant species in the catch which have been defined as "pollock-majority-data" and 2) all-data rec- ords. Based on records from five vessels class-gear types, it was determined that ADIs resulting from the two procedures were statistically the same in 80% of the cases studied because of high proportion of pollock in catches. However, in certain area-time cells where other species formed a relatively high proportion of the catch, the two procedures resulted in lower ADIs. Therefore, use of data only from pollock-majority-data may cause abundance to be overestimated while use of all-data may cause it to be underestimated because some of the effort may have been directed to another species. Thus, ADIs calculated by either method may be biased towards the high or low side and may not be directly comparable from year to year. In an attempt to reduce such bias in ADIs, four area- time cells were identified as potential index areas for abundance computations. Three of these four cells turned out to be good index areas for pollock. The ADI procedure used thus resulted in an extension to the orig- inal ADI procedure by Doi et al. (1972) to include: 1) selection of vessel-gear categories that were most repre- sentative of pollock fishing activities and 2) selection of area-time cells that provided good indexing areas. Since then, the study has been updated to include data analyses from 1964 to 1978. Trends in CPUE and ADI show that from 1964 to the early 1970s, there was a general increase in the abundance of pollock. This trend was the result of increased pollock abundance and fishing power of vessels. However, we cannot determine the separate effect of these two factors. For 2-3 yr during the early 1970s, abundance of pollock appeared to be at peak levels. Beginning in 1972, both CPUE and ADI trends decreased but stabilized during 1975-78 at an intermediate level when 1.1 million t of walleye pollock were harvested annually. ACKNOWLEDGMENTS The International North Pacific Fisheries Com- mission and the Fisheries Agency of Japan were instru- mental in organizing the working group study which resulted in this report. We wish to thank Yoshiya Takahashi, Takashi Sasaki, Koya Mimura, Koji Imamura, and Yasuho Tadokoro for their assistance and advice during the workshop. LITERATURE CITED BAKKALA, R.. W. HIRSCHBERGER, and K. KING. In press. The groundfish resources of the eastern Bering Sea and Aleutian Islands Region. Mar. Fish. Rev. DOI, T., K. Y. MUN, K. TAKAO, K. ISHIOKA, and K. OKADA. 1972. Stock assessment of the Kuruma-prawn Penaeus japomcus Bate in Hiuti-Nada Area of the Seto Inland Sea. [In Jpn., Engl, abstr.) Bull. Tokai Reg. Fish. Res. Lab. 69:45-54. FOOD A.\D AGRirUl.Tl'RE ORGANIZATION. 1976. Monitoring of fish stock abundance: The use of catch and ef- fort data. FAO Fish. Tech. Rep. 155, 101 p. FORRESTER, C. R., A. J. BEARDSLEY, and Y. TAKAHASHI. 1978. Groundfish. shrimp, and herring fisheries in the Bering Sea and Northeast Pacific — Historical catch statistics through 1970. Int. North Pac. Fish. Comm. Bull. 37, 147 p. INTERNATIONAL NORTH PACIFIC FISHERIES COMMISSION. 1979. Annual report 1976. 115 p. LOW, L. L. 1974. A study of four major groundfish fisheries of the Bering Sea. Ph.D. Thesis, Univ. Washington, Seattle. 256 p. SNEDECOR, G. W., and W. G. COCHRAN. 1967. Statistical methods. 6th ed. The Iowa State Coll. Press, .Ames, Iowa. .59.'i p. 11 NOAA TECHNICAL REPORTS NIWS CIRCULAR AND SPECIAL SCIENTIFIC REPORT- GUIDELINES FOR CONTRIBUTORS -FISHERIES CONTENTS OF MANUSCRIPT First page. Give the title (as concise as possible) ol the paper and the author's name, and footnote the author's affiliation, mailing; address, and ZIP code. Contents. Contains the text headings and abbreviated figure legends and table headings. Dots should follow each entry and page numbers should be omitted. Abstract. Not to exceed one double-spaced page. 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